As more and more information is moving into electronic form, encryption is becoming more common. One prior art method of encryption is public key encryption—an encryption scheme in which each person gets a pair of keys, called the public key and the private key. Each person's public key is published while the private key is kept secret. Messages are encrypted using the intended recipient's public key and can only be decrypted using the recipient's private key. Messages are signed using the sender's public key and can only be decrypted using the sender's public key. The need for sender and receiver to share secret information (keys) via some secure channel is eliminated—all communications involve only public keys, and no private key needs to be transmitted or shared. Public-key cryptography can be used for authentication (digital signatures) as well as for privacy (encryption). Other encryption schemes, such as symmetric key encryption rely on an exchange of keys.
FIG. 1 is a diagram of a prior art network. The client 110 connects to a server 130 through network 140. A certification authority 150 provides a private/public key pair for the user. The certification authority 150 further provides certificate 115 to the client. The certificate 115 is a copy of the user's public key, signed by the certification authority 150, to prove its authenticity. The certificate 115 and the user's private key 120 are stored on the client system 110. Private keys generally are 64 bit numbers or larger and users do not memorize their keys. Because computer systems are rarely truly secure, the key may be taken from a computer system. In order to prevent this, the key may be stored in a password protected file. However, passwords may be broken. Additionally, the system is only as secure as the least secure level. For one embodiment, the user types in the password 125, to release the private key 120, so the user can use the private key.
Client II 160 illustrates the same user roaming, i.e. on a different computer system, connecting to a server 130 through the network 140. Client II 160 does not have the user's private key or certificate. Therefore, the user has to carry a smart card or diskette 170 on which the user's certificate and private key are stored. Again, the certificate and private key may be protected by a password. However, smart cards can be lost, and require a user to remember to carry something.
Furthermore, generally the keys are stored on a computer system, and are thus connected to the computer system, rather than an actual user. In the prior art, a user could pass to an impostor his or her password, accidentally or on purpose, and that impostor could then “prove” that he or she was the user.
Furthermore, because each user's private key is stored on his or her computer system, administering the keys is difficult.
In addition, a single mistake, i.e. accidentally granting access to an unauthorized user, permanently breaches the security of the private-public key pair, since the private key is revealed.